For many years, it has been known to use a stabilizer or a reamer, or both in combination, in association with a drill bit as part of the drill string used in drilling a hole in the ground such as in the drilling of an oil well. The stabilizer reduces the lateral movement of the drill bit as it works its way through rock formation.
The function of the reamer is to maintain the diameter of the hole as the drill bit proceeds downwardly through the rock formation. As the oil well hole is being drilled, the rock drill bit gradually wears to undersize and thus the hole which is cut gradually becomes of undersize diameter. The function of the reamer, which has a hardened surface, is to grind the circumference of the hole, shortly after it has been cut by the rock drill bit, and thus keep the hole diameter to size.
Numerous stabilizer and reamer designs are disclosed in the prior art. Some are disclosed in the following list of United States patents:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 2,419,901 W. G. Lake April 30, 1945 2,708,104 D. C. McAllister Nov. 22, 1950 3,575,247 Robijn Feenstra April 20, 1971 3,851,719 Thompson et al. Dec. 3, 1974 4,073,354 Rowley et al. Feb. 14, 1978 4,140,189 Garner Feb. 20, 1979 4,190,124 Terry Feb. 26, 1980 ______________________________________
A well-known and widely used stabilizer-reamer is sold under the trade mark SR3 by Christensen Corporation, Salt Lake City, Utah. This stabilizer-reamer has an upper section which acts as the stabilizer. Vertical spiral grooves are present therein for permitting drilling mud and cut rock chips to pass upwardly through the annular space between the drill bit and the wall of the hole. The lower section of the stabilizer-reamer has countersunk therein three or more vertically disposed roller-cutters with hardened buttons embedded in the surface of the roller cutters. One problem with these roller cutters is that under the severe stress and shock conditions encountered in drilling through a rock formation, the pins upon which the rollers rotate become worn with time. Indeed, in some cases, the pins may eventually break away from the reamer section of the stabilizer-reamer and fall down the hole. One or more of the rollers may also fall down the hole. This is a very serious and costly problem because the rollers and pins at the bottom of the hole prevent the drill bit from biting the rock and cutting the hole. The only way to effectively deal with the problem is to make a trip by withdrawing the drill bit from the hole and then send expensive fishing equipment down the hole in order to grasp and withdraw the roller and pin from the hole.
Another problem with the roller cutters is that because they wear quickly, they do not last the length of time that it takes to drill the hole to total depth. Consequently, during several of the numerous trips that are made in the drilling of an oil well, the rollers must be replaced, thereby causing expensive maintenance time.
A recent development in rock drill bit design, replacing the traditional tri-cone bit, in some cases, has been the inverted conical style. Such inverted conical bits are manufactured and sold under the trade mark TRI-MAX by International Petroleum Engineering Corporation, Norman, Okla. The advantage of these bits is that they purportedly last longer in the hole and drill faster, particularly through limestone formations. One problem with the inverted conical type bit, however, is that it tends to deviate laterally from the vertical, as the hole is being drilled. Keeping these bits more or less on line, therefore, has presented somewhat of a problem.